Far-infrared laser system for detection of defects in polyethylene-insulated power cables

A far-infrared laser system has been constructed and used for real-time detection of voids and contaminants imbedded in the polyethylene insulation of moving power cables. The measured scattered FIR laser radiation can be correlated to the size and the shape of the defects in polyethylene insulation during extrusion. The smallest detectable defect is 25 μm in size, which produces a scattered signal at a level about five times the background radiation scattered from microvoids usually occurring in cross-linked polyethylene material at a number density of 109 per cc.